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422 Chapter 6: Routing
Table 6-29 lists several definitions of terms covered throughout the chapter.
Table 6-29
Definitions Covered in This Chapter
Term
Definition
Link-state protocol
A type of logic used by a routing protocol, characterized by exchanges
of full topology information, which is processed with the Dijkstra
algorithm to form a shortest-path tree to determine routes. OSPF is an
example.
Distance vector
A type of logic used by a routing protocol, characterized by exchange
of a vector consisting of the destination network and a metric. IP RIP,
IPX RIP, and IGRP are examples of distance vector routing protocols.
Route poisoning
A distance vector feature of advertising routes that were previously
good but that are now failed, with a metric value that is considered to
be infinite. This is a loop-prevention feature.
Flash updates
A distance vector feature of sending new or changed routing
information in an update immediately rather than waiting on the next
update timer to expire.
Triggered updates
Another term for flash updates.
Update timer
A distance vector feature that defines the interval between sending
routing updates. A neighboring router will believe that a neighboring
router has failed if updates are not received after some multiple of the
update timer (usually 3).
Holddown timer
A distance vector feature that defines how long to wait to update a
route for a particular subnet, after hearing that the route that was
previously in the routing table has failed.
Split horizon
A distance vector feature that prevents the routing protocol from
advertising routes out an interface if the routes were learned from
updates entering that interface.
Split horizon with poison
reverse
A variation of split horizon. Routes learned via updates entering an
interface are advertised in updates sent out that same interface, except
that these routes are given an infinite distance metric.
ch06.fm Page 422 Monday, March 20, 2000 5:11 PM